Electron optic system utilizing a focusing electrode having a more positive voltage than the two adjacent electrodes

ABSTRACT

A system wherein spherical aberration is reduced in an electronoptic device having post deflection acceleration by connecting the focusing electrode of an &#39;&#39;&#39;&#39;einzel&#39;&#39;&#39;&#39; type electrostatic electron lens to a unitary source of potentials at a potential more positive than the potential connected to the electrodes disposed on either side of the focusing electrode. In every case, the same supply above mentioned provides all the potentials necessary to operate the device.

nited States Patent Amboss 1 Jan. 30, 1973 54 ELECTRON OPTIC SYSTEM 3,023,336 2/1962 Frenkel .315/31 TV UTILIZING A FOCUSING ELECTRODE HAVING A MORE POSITIVE VOLTAGE FOREIGN PATENTS OR APPLICATIONS THAN THE TWO ADJACENT 527,567 10/1940 Great Britain ..3l5/l6 ELECTRODES C O f h Primary Examiner arl D. uar ort [76] Inventor E z i b i g Assistant Examiner-J. M. Potenza i Attorney-S0kolski& Wohlgemuth [22] Filed: Oct. 20,1970 [2i] Appl. N0.: 82,477 [57] ABSTRACT A system wherein spherical aberration is reduced in an electron-optic device having post deflection ac- [5?] $5.81. ..3l5/31Hl;,l 3l5/l5 Cccration by Connecting the focusing electrode of an ueinze e ectrostatic electro ens to a unita y l I 0 can 15/ 3 17 source of potentials at a potential more positive than the potential connected to the electrodes disposed on [56] References C'ted either side of the focusing electrode. In every case,'the

UNITED STATES PATENTS same supply above mentioned provides all the poten 3 tlals necessary to operate the device. Y 2,363,359 11/1944 Ramo l5/3l R 3,049,641 8/l962 Gleichauf ..315/3l TV 5 Claims, 3 Drawing Figures Power 4 Supply (PRIOR ART) PAIENTEDJANIBO I975 3, 714,504

Kurt Amboss,

INVENTOR.

,M/MZ

ATTORNEY.

ELECTRON OPTIC SYSTEM UTILIZING A FOCUSING ELECTRODE HAVING A MORE POSITIVE VOLTAGE THAN THE TWO ADJACENT ELECTRODES BACKGROUND OF THE INVENTION The background of the invention will be set forth in two parts.

1. Field of the Invention The present invention pertains generally to the field of electron-optics and more particularly to a system including an electron-optic device including an electrostatic electron lens of the einzel type which derives its potential from a single power supply.

2. Description of the Prior Work In the past, electron optical devices such as cathode ray tubes of a relatively high brightness, for example, consisted of a cathode electrode, emitting a stream of electrons through an apertured electrode suitably biased to control the emitted current, and one or more electrodes by means of which the electrons were raised to a high kinetic energy and focused onto a fluorescent screen downstream. In some cases, the task of focusing was left to a magnetic electron lens external to the vacuum envelope of the device.

The accelerating and focusing electrodes or magnetic lens were followed by transverse electric or magnetic fields which were used to deflect the electron beam over the face of the fluorescent screen.

A wide variety of arrangements of the focusing electrode and of the voltages impressed on them have been used to focus the stream of electrons onto the fluorescent screen. However, an arrangement which has found so much acceptance that it has been almost universally adopted, consists of a set of three electrodes in the form of cylinders or diaphragms, with the outer electrodes maintained at the same potential. This type of lens is often referred to as an einzel" lens as described in a book entitled Electron Optics by O. Klemperer, Cambridge University Press, Cambridge, England 1953) at page 64. In the case where the inner electrode is connected electrically to the cathode so that in essence only one voltage is applied, such lenses have become known as unipotential or univoltage lenses.

Although the focusing actions of such lenses have been known to take place where the inner electrode is at a potential above that of the outer electrodes, the einzel lens has not been used in this manner since a source of higher voltage has to be available. This prejudice in the art is evidenced by the statement Moreover for the realization of voltage ratios, V /V,, I an additional high voltage supply is needed, made by K. J. Hanszen and R. Lauer in the text titled Focusing of Charged Particles, edited by A. Septier, Academic Press, New York (1967).

There exists, however, a number of electron optical devices in which the necessary higher voltage is present for other reasons. One such device, for example, is the post deflection acceleration cathode ray tube. In this tube an additional voltage is applied, usually distributed over some distance, beyond the focusing and reflection element in order to reduce the power required for deflection. In such devices invariably the practice has been to operate the center element of the einzel" lens near the potential of the cathode.

Although the einzel lens focuses with its center electrode above or below that of the other elements, it does so with reduced aberration when the center electrode is positive, since the electrons are accelerated toward the axis into a more uniform region of the electric field.

Because einzel lenses often have the center electrodes tied to the cathode to operate as unipotential lenses, and because the necessary high voltage is not often available, a general but strong prejudice developed in the art wherein an arrangement having the focusing element operated at a higher positive potential than its adjacent lens electrode was always associated with the requirement of a separate high voltage power supply. Thus, when the newer post deflection acceleration technique was developed allowing higher image intensity without requiring a separate relatively higher potential power source, those working in this art continued the practice of providing the focusing element or anode with a potential lower than that of the other electrostatic lens element.

It should therefore be evident that a new technique which overcomes this disadvantageous prejudice in the art and operates the focusing element at a higher positive potential than the remainder of the lens elements in a system using only a single power supply, constitutes a significant and extremely useful advancement of the electron-optic art.

SUMMARY OF THE INVENTION In view of the foregoing factors and conditions characteristic of the prior art, it is a primary object of the present invention to provide a new and improved electron-optic system not subject to the disadvantages enumerated above and which includes a means whereby aberrations of a charged particle beam system are improved.

It is another object of the present invention to provide an electron-optic system which is well adapted for use with oscilloscope cathode ray tubes employing post deflection acceleration. I

It is still another object of the present invention to provide a unique yet simple electron-optic system which effectively reduces the emitted charged particle trajectory excursion from the axis without the use of a separate high voltage power supply.

It is yet another object of the present invention to provide an electron-optic system which includes an electron-optic device having an electrostatic electron lens of the einzel type which may be used in color and black and white cathode ray tubes as well as in electron and ion accelerators for electron irradiation and ion implantation, for example.

According to one aspect of the present invention, reduced aberration is provided in an electron-optic system including a unitary potential source with a cathode potential V an electron lens potential V 'a focusing electrode potential V and a second anode or screen potential V The system also incorporates an electron-optic device including a cathode electrode electrically connected to V and a final acceleration electrode electrically connected to V which is a greater positive potential than V Further, an electrostatic electron lens of the einzel type is disposed between the cathode and the final acceleration electrode and includes electrodes on either side of a focusing electrode which are electrically connected to V which is a greater positive potential than V but less than V The positive potential V p electrically connected to the focusing electrode is also greater than V but not more than V The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by making reference to the following description taken in conjunction with the accompanying drawing in which like reference characters refer to like elements in the several views. It should be understood that while a system incorporating post deflection acceleration is illustrated, other systems not utilizing such an arrangement may incorporate and benefit from the principles of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial diagrammatic sectional view of a prior art cathode ray tube having a unipotential focusing type electrostatic lens and post deflection acceleration;

FIG. 2 is a schematic representation illustrating an electrostatic lens electrode power supply interconnection providing reduced spherical aberration in a system utilizing a single power supply and an electro-optic device incorporating post deflection acceleration and a unipotential focusing type electrostatic lens; and

FIG. 3 is a graph showing typical excursions R of the trajectory from the beam axis along the length of trajectory Z for a unipotential lens operating with its focus electrode potential V less and greater than the potential V on the other elements of the lens.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring again to the drawing and more particularly to the prior art system illustrated in FIG. 1, there is shown a cathode ray tube 11 with an outer glass envelope 13 having a neck portion 15 and a screen portion 17. An electron beam generated in an electron gun 19 by a cathode 21 is controlled or modulated by a control grid or element 23 before being initially accelerated and focused by an einzel" type electrostatic lens including an electrode 25, a focusing electrode 27, and a further electrode 29.

The beam is then deflected by appropriate potentials on vertical deflection plates 31 and on horizontal deflection plates 33 as is widely known in the art through deflection circuits not shown. Once deflected, the beam is influenced by a positive potential applied to a post deflection electrode which may take the form of a resistive coating 35 on the inner surface of the glass envelope 13 between the neck portion 15 and the screen portion 17. The beam is attracted toward the screen area having a phosphorous coating 37 on the inner surface thereof by an even higher positive potential V provided at a second anode 39 (generally the termination of the resistive coating) located at or adjacent the screen portion 17.

As can be seen from this figure, a single power supply 41 provides all the necessary potentials by the use of a single voltage divider network 43 having fixed and variable type connections thereon. Thus, in the order of increasing positive potential, the network 43 provides a modulation electrode potential V a cathode potential V a focus electrode potential V lens and post deflection acceleration electrode potentials V and V and i finally the second anode potential V It will be noted that according to the prior art the focus electrode 27 is electrically connected to the V variable tap on the voltage divider 43 providing to this electrode a potential more positive than the cathode potential V but less than the potential V and V p applied to the adjacent lens electrodes 25 and 29. This system provides a beam excursion vs. beam length comparison as illustrated by the dashed lines 45 in FIG. 3. It can easily be seen that in the region between Z and Z, the excursion increases considerably, which causes a significant degree of aberration in the image present on the screen.

In accordance with the present invention, and overcoming the long established prejudice in the art of only furnishing the focusing electrode with a lower potential than provided to the other lens electrodes has been overcome, and FIG. 2 shows that a voltage divider network 43A is connected across a single or unitary power supply 41 A and that the focusing electrode 27A is electrically connected to an adjustable contact V on a voltage divider network 43A to provide this element of the electrostatic lens with a more positive potential than V on the cathode 21A and also V at the other adjacent lens electrodes 25A and 29A.

This technique produces the clearly advantageous result indicated by the solid line 47 shown in the graph of FIG. 3. In this mode of operation the lens exhibits significantly reduced aberration which is typically of the order of 30 percent.

From the foregoing it should be evident that the present invention overcomes a formidable prejudice in the electron optic art and teaches that the focus element in an electrostatic lens of the einzel type may be advantageously provided with a greater positive potential than provided to adjacent elements of a lens where a single power supply is used to produce all the operational voltages necessary for the electron optic device.

Although specific structures and embodiments have been described in detail, it should be obvious that other similarly functioning structures and embodiments may be substituted for the ones described. For example, the principles of the present invention may be applied to a color television tube having a shadow mask or grill wherein these electrodes operate at a potential lower than that of the tube's screen or final anode.

What is claimed is:

1. An electron-optic system exhibiting reduced aberration, comprising:

a single power source providing a cathode potential V an electron lens potential V a focusing electrode potential V,.-, and a final anode potential V and an electron optic device including a cathode elec trode connected to said V and a final acceleration electrode connected to said V which is a greater positive potential than said V said device also including an electrostatic lens of the einzel type which is disposed between said cathode and said final acceleration electrode and including lens electrodes disposed on either side of a focusing electrode and electrically connected to said V which is a greater positive potential than said V but less than said V said focusing electrode being electrically connected to said V,-, which is a greater positive potential than said V but not more than said V 2. An electron-optic system according to claim 1, wherein said electron optic device includes a post deflection acceleration electrode and wherein said lens electrodes are electrically connected to said post deflection acceleration electrode.

3. An electrostatic optic system according to claim 1, wherein said lens electrodesand said focusing electrode are centrally apertured conductive elements 

1. An electron-optic system exhibiting reduced aberration, comprising: a single power source providing a cathode potential VC, an electron lens potential VL, a focusing electrode potential VF, and a final anode potential VS; and an electron optic device including a cathode electrode connected to said VC, and a final acceleration electrode connected to said VS, which is a greater positive potential than said VC, said device also including an electrostatic lens of the ''''einzel'''' type which is disposed between said cathode and said final acceleration electrode and including lens electrodes disposed on either side of a focusing electrode and electrically connected to said VL which is a greater positive potential than said VC, but less than said VS, said focusing electrode being electrically connected to said VF, which is a greater positive potential than said VL, but not more than said VS''.
 1. An electron-optic system exhibiting reduced aberration, comprising: a single power source providing a cathode potential VC, an electron lens potential VL, a focusing electrode potential VF, and a final anode potential VS; and an electron optic device including a cathode electrode connected to said VC, and a final acceleration electrode connected to said VS, which is a greater positive potential than said VC, said device also including an electrostatic lens of the ''''einzel'''' type which is disposed between said cathode and said final acceleration electrode and including lens electrodes disposed on either side of a focusing electrode and electrically connected to said VL which is a greater positive potential than said VC, but less than said VS, said focusing electrode being electrically connected to said VF, which is a greater positive potential than said VL, but not more than said VS''.
 2. An electron-optic system according to claim 1, wherein said electron optic device includes a post deflection acceleration electrode and wherein said lens electrodes are electrically connected to said post deflection acceleration electrode.
 3. An electrostatic optic system according to claim 1, wherein said lens electrodes and said focusing electrode are centrally apertured conductive elements aligned with said cathode electrode.
 4. An electron-optic system according to claim 1 wherein said unitary power source includes a voltage dividing network providing all the output potentials of said power supply. 